The disclosure of Japanese Patent Application No. 12-138586 filed on May 11, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a control apparatus of a hybrid vehicle and, more particularly, to an improvement in a hybrid vehicle control apparatus that is capable of reducing the shock caused by torque fluctuations during speed shifts in a hybrid vehicle that has a stepwise variable transmission capable of automatically performing speed shifts without employing a torque converter.
2. Description of Related Art
Recently, hybrid vehicles (hereinafter, referred to as xe2x80x9cHVsxe2x80x9d) equipped with a hybrid system having great advantages in environmental protection and fuel economy improvement are being researched, developed and commercialized. An HV system is a power train that incorporates a combination of two kinds of drive power sources, such as an internal combustion engine (hereinafter, simply referred to as xe2x80x9cenginexe2x80x9d) and an electric motor (normally, a motor-generator (referred to as xe2x80x9cMGxe2x80x9d)) performing both the function of an electric motor and the function of a generator-motor (electric power generator). By selectively using the engine and the electric motor in accordance with the driving condition, the hybrid system can compensate for disadvantageous aspects of the two drive power sources while fully exploiting the advantages of the two drive power sources, so that smooth and highly responsive power performance can be achieved. This type of HV is equipped with a battery for driving the MG as an electric motor. The battery is charged by performing regenerative power generation through the use of the MG as a generator during deceleration of the vehicle.
Transmissions that can be employed in the aforementioned HVs include a continuously variable transmission capable of continuously changing the speed ratio while receiving torque from the engine and a stepwise variable transmission capable of discretely changing the speed ratio simultaneously with temporary discontinuation of torque from the engine. Some stepwise variable transmissions employed in HVs perform torque transfer using a torque converter, and some other stepwise variable transmissions torque transfer using a friction clutch. Among these transmissions, a stepwise variable transmission employing a friction clutch (hereinafter, referred to as xe2x80x9cclutch-equipped stepwise variable automatic transmissionxe2x80x9d) is being considered in various ways for commercialization as a transmission that is simple in construction and control and is suitable to HVs.
The aforementioned clutch-equipped stepwise variable automatic transmission automatically engages and disengages the clutch and performs speed-shifting based on the vehicle speed or the amount of depression of an accelerator pedal caused by a driving person (accelerator operation amount). Thus, the clutch-equipped stepwise variable automatic transmission realizes easy shifting that does not require a driving person to operate a clutch pedal or the like, at a relatively low cost.
In some cases, however, while the HV is running at a constant acceleration (i.e., the HV is gradually accelerating with a constant amount of accelerator operation), the clutch-equipped stepwise variable automatic transmission performs a shift from a low speed side to a high speed side based on, for example, the vehicle speed and the amount of accelerator operation. In such a case, the clutch is automatically disengaged to start a shifting operation although a driving person does not intend the operation (although a driving person does not change the amount of accelerator operation or the like). In this case, the disengagement of the clutch temporarily discontinues drive torque, and therefore the HV decelerates.
As a result, a deceleration shock is caused by torque fluctuation, thus discomforting the driving person.
An HV speed shift control apparatus for reducing the deceleration feel (deceleration shock) through torque assist achieved by increasing the drive torque of the electric motor (MG) simultaneously with disengagement of the clutch is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-69509.
If the running of the HV is controlled through coordination between the drive torque of the engine and the drive torque of the electric motor (MG), the control described in Japanese Patent Application Laid-Open No. 11-69509 is able to avoid complete depletion of drive torque from the entire HV since a drive torque of the HIV can be secured by the torque assist from the electric motor, despite elimination of engine torque. However, at the time of disengagement of the clutch, a sharp torque assist provided by the electric motor causes another torque shock, resulting in insufficient eradication of the discomfort to a driver.
The invention has been accomplished in view of the aforementioned problems. It is an object of the invention to provide a control apparatus for a hybrid vehicle capable of reducing a deceleration shock caused by torque fluctuation during a speed shift and reducing the discomfort perceived by a driving person.
To achieve the aforementioned object, the invention provides a control apparatus for a hybrid vehicle having an internal combustion engine, a stepwise variable transmission capable of automatic shifting, a clutch that is disposed between the internal combustion engine and the stepwise variable transmission and that discontinues and establishes a power transfer between the internal combustion engine and the stepwise variable transmission, and an electric motor that is disposed between the stepwise variable transmission and a drive wheel and that drives the drive wheel and performs regenerative power generation using the drive wheel., The control apparatus comprises a shift control means for performing a control of performing a shifting operation of the stepwise variable transmission at a start of elimination of a drive torque of the internal combustion engine caused by disengaging the clutch, and of recovering the drive torque of the internal combustion engine by re-engaging the clutch, when the hybrid vehicle is running coordinately by the drive torque generated by the internal combustion engine and a drive torque generated by the electric motor; and a motor control means for performing a control of increasing and decreasing the drive torque of the electric motor based on a predicted automatic shifting operation.
Therefore, the control of increasing and decreasing the drive torque of the electric motor is performed in accordance with the timing of the automatic shifting operation of the stepwise variable transmission. Hence, fluctuation of the entire drive torque of the vehicle caused at the time of elimination of the drive torque of the internal combustion engine is controlled and thereby reduced, so that the deceleration shock can be reduced.